In a mobile communication system, a radio terminal performs a handover from a source cell to a target cell. The radio terminal performs a random access procedure with the target cell during the handover. The random access procedure may be referred to as RACH (Random Access Channel) procedure.
The random access procedure includes a process of transmitting, by the radio terminal, a random access preamble to the target cell, and a process of receiving, by the radio terminal, a random access response from the target cell. The random access response includes an uplink grant indicating an uplink radio resource allocated to the radio terminal in the target cell, and a timing advance value to be applied to an uplink transmission to the target cell (transmission timing adjustment value).